FIG. 13 exhibits a prior device for fixing a handle stem.
A fork stem 10 provided on a front fork 1 is inserted into a head pipe 20 of a skeleton frame 2. The fork stem 10 is rotatably mounted in the head pipe 20 by an upper bearing 13 and a lower bearing 14. There is a space between an inner surface of the upper bearing 13 and an outer surface of the fork stem 10. A taper ring 31 is inserted into the space as if it were a wedge. Thus, the head pipe 20 is kept concentric to the fork stem 10. On the other hand, a handle stem 3 consists of a stem-binding cylinder 30 coupling on the fork stem 10 and an arm 38 projecting about horizontally toward a handle bar 356. The binding cylinder 30 has a pair of tightening ears which face each other with a small clearance 72. The tightening ear 70 is perforated by a through hole and the other tightening ear (not illustrated in FIG. 13) is perforated by a threaded hole. The through hole and the threaded hole are arranged coaxially. A bolt 8 penetrates the through hole and the threaded hole in the tightening ears facing each other.
The conventional coupling of the handle stem to the frame 2 will be explained now. The upper bearing 13 and the lower bearing 14 are mountained at both ends of the head pipe 20. And then the fork stem 10 is inserted into the head pipe 20. The top of the fork stem 10 projects out from the upper end of the head pipe 20.
Next, the taper ring 31 is put on the fork stem and a lower part of the taper ring 31 is pushed into the space between the outer surface of the fork stem 10 and the inner surface of the upper bearing 13 as if it were a wedge. And a ring 33 and the binding cylinder 30 of the handle stem 3 are put on the fork stem 10. A screw cap 4 is engaged with a threaded inner surface 105 formed at the upper end portion of the fork stem 10. The cap has a flange 41 at an outer periphery thereof. When the screw cap 4 is screwed into the fork stem 10, the flange 41 presses the top end of the stem-binding cylinder 30. Thus, the stem-binding cylinder 30 is fixed on the fork stem 10 in the axial direction thereof. At the same time, the ring 33 and the taper ring 31 are forced down by the binding cylinder 30, and the taper ring 31 is pushed into the space between the outer surface of the fork stem 10 and the inner surface of the upper bearing 13. Thereby the upper bearing 13 is kept concentric to the fork stem 10. And the upper and lower bearings 13, 14 are not shaky because they are pushed down by the taper ring 31 and the head pipe 20.
Finally, the bolt 8 penetrates the holes in the tightening ears facing each other with a small clearance 72. The threaded hole in one of the tightening ears is engaged with the bolt 8. Then, when the bolt 8 is tightened, the clearance 72 decreases. As the result, the diameter of the stem-binding cylinder 30 becomes smaller. Therefore, the outer surface of the fork stem 10 is pressed by the inner surface of the stem-binding cylinder 30. In other words, the stem-binding cylinder 30 is fixed on the fork stem 10 so that the binding cylinder 30 may not rotate on the fork stem 10.
According to the aforementioned prior device, however, there is a problem in that the stem-binding cylinder 30 cannot be bound and fixed to the fork stem 10 rapidly and certainly.
The reason for this is that, in the conventional coupling, both the inner surface of the binding cylinder 30 and the other surface of the fork stem 10 are smooth surfaces and the coefficient of friction between the above mentioned two surfaces is left out of consideration.
Accordingly, it is necessary to enlarge the binding force of the stem-binding cylinder against the outer surface of the fork stem 10 in order to join two members together in a stable state.
A purpose of this invention is to provide a handle stem fixing device which improves the fixing power of the stem-binding cylinder to the fork stem.